What is stopping my washing machine from starting?

I have an Indesit WIL103 washing machine approx 2 years old, never had problems with it until recently.
Firstly it jumped about violently - I stopped it, drained the water and removed drain pump, flushed drain hose, checked rubber sump - I found some coins to remove.
Put it back together and started machine - got error lights 1 and 2 flashing along with a rapid flashing door lock light - looked these codes up and came back with 'communication error'.
Removed pcb which contains led's, program selector etc from top of machine. Cleaned up contacts where the (only) plug fits onto the board, result - 'communication error' has gone.
Started machine - door lock will not work, no door lock red led lit, no physical lock movement either.
Bought a new door interlock (£12), fitted it and still the same. Checked for AC in connector that fits to door interlock - results are AC on 1st and 3rd pins but nothing on middle pin. Does the middle pin suppose to have AC running to the door interlock or is it there to complete a loop and recieve AC from either of the other pins when the door lock actuates?
Apart from tracing the wire (middle pin) back to its other end, checking for continuity etc - what connects to the other end and why is it stopping my machine from working?
I would be so happy to not wash clothes by hand in the bath if someone could enlighten me!!